As optical communications are gaining entry into the fields of subscriber-loop and local-area networks, increased attention is being paid to the feasibility of substrate-supported waveguides as forming predefined optical paths in couplers and between optical component devices such as, e.g., light sources and detectors on a common substrate. Considered as eminently desirable in this respect are means for forming low-loss waveguides which are suitable for side-by-side coupling.